[Rachel's Introduction: What is your family's personal environmental impact and what does it cost?]

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By Jennifer Openshaw

NEW YORK (MarketWatch) -- Go green. It's in the news all the time now. Reduce global warming, save the planet, do the right thing. But how -- and how much? New carbon-footprint measures help you know.

Carbon dioxide. Otherwise known as CO2, or "greenhouse gas," it's the main byproduct of burning fossil fuels and the main culprit in global warming and climate change.

Some climate scientists say that if we don't cut our emissions in half by 2050, we face an outcome that makes the end-of-the-world movies "I Am Legend" and "Children of Men" look like Tom and Jerry cartoons. OK, maybe I'm exaggerating a little.....

Someday you'll have to ...

Your "carbon footprint" represents the amount of CO2 you emit in daily life -- driving, living at home, traveling, eating and so forth.

That's important. Right now, carbon footprints signal your contribution to the problem. Beyond that, they give an idea of how much energy you consume. That has obvious financial implications, and we're running out of the stuff.

And I expect someday, somehow we'll all have to pay directly for our carbon footprints -- through a tax or through so-called "cap and trade" programs that force the most serious polluters to pay more for the privilege. I don't know how it's going to happen, but I bet it does happen.

Measuring your footprints

There's a growing set of Web-based calculators to help you easily and quickly determine -- and interpret -- your carbon footprint. I checked out a few.

The best I found wasn't where I thought it would be -- it was at an oil company Web site! Specifically, it's on BP.com's "Environment and Society" page. Visit the site.

Here's why I liked it, and what I found out:

Complete picture. BP's calculator gives you tons ("tonnes") of CO2 emitted per year from household energy use, ground travel, air travel and waste production. It then asks questions about your home, personal and business travel

Realistic. BP's site isn't just about energy consuming devices -- it's about behavior too. Like many calculators, BP asks if you have compact fluorescent bulbs. But it also asks if you turn off lights or take showers instead of baths! I found out that I save a ton of CO2 each year just by turning off lights when I leave a room.

Interactive. The site gives you a chart diagramming CO2 emissions in the four categories noted above. Each time you answer a question, you can see the chart change. It's pretty cool to know how every aspect of your life affects emissions. If I traded my SUV for an ordinary car, I'd save 2.5 tons of emissions at 12,000 miles per year. As we'll learn in a minute, that's about 10% of my total.

Unfortunately, I'm above average. With a detached home, family, 2 cars and 10 round-trip long-haul business trips a year, I'm responsible for 24 tons of CO2 emissions. How bad is that? The average U.S. family emits 18.58 tons. And they also mention that would fill about 2 1/2 Olympic-sized swimming pools. Good thing I didn't tell it how often I really travel by air....

Taking lighter footsteps

Clearly, we have shared responsibility for reducing greenhouse gases.

And I'm no dummy -- I know most of this CO2 starts life as petroleum- based fuels, which cost a lot of money and have all kinds of other bad effects both political and environmental.

Hats off to those making it easy to learn the effects of my ways. And making it easier to do something about it.

It's worth 15 minutes of your time to do the same.

Peter Sander contributed to this article.

Jennifer Openshaw is the author of "The Millionaire Zone" and CEO of Openshaw's Family Financial Network. She hosts ABC Radio's Winning Advice and serves as an adviser to some of America's top corporations.